1. Field of the Invention
The present invention relates to a volume adjusting apparatus and a volume adjusting method for preventing sound leakage.
2. Description of the Related Art
Recently, portable playback apparatuses capable of play back musical tunes outside the home or outdoors have been widely used. As shown in FIG. 16, a headphone 102 is connected to a playback apparatus 101 according to the related art. A user listens to a musical tune recorded in the playback apparatus 101 through the headphone 102. The playback apparatus 101 has an operation unit for starting and stopping playback of a musical tune and for volume adjustment. The user operates the operation unit, thereby being able to adjust the playback volume of the musical tune.
For example, when a user plays back a musical tune in a “running” train using such a playback apparatus, the user operates the operation unit to turn up the volume so that the user can appropriately listen to the musical tune since ambient noise is loud. When the train “stops”, the user turns down the volume since the ambient noise becomes smaller than that generated when the train is “running”.
A playback method of the playback apparatus 101 according to the related art will be described with reference to a flowchart shown in FIG. 17. At STEP S101, the playback apparatus 101 is turned ON. At STEP S102, a musical tune recorded in the playback apparatus 101 is played back.
At STEP S103, whether to adjust the volume is determined. For example, when the musical tune is hardly heard due to the ambient noise and it is determined that the volume is to be adjusted, the process proceeds to STEP S104. At STEP S104, the user operates the operation unit to set the volume. If it is determined that the volume is not to be adjusted, the process proceeds to STEP S105.
At S105, whether the user continues to listen to the musical tune is determined. If it is determined that the user continues to listen to the musical tune, the process returns to STEP S102. At STEP S102, playback of the musical tune is continued. If it is determined that the user does not continue to listen to the musical tune, the process proceeds to STEP S106. At STEP S106, the playback apparatus 101 is turned OFF. The process then terminates.
As described above, in the playback apparatus according to the related art, the user recognizes the surrounding ambient noise and manually adjusts the volume based on the recognition so that the user can appropriately listen to a musical tune.
However, when the volume is adjusted manually in such a manner, sound leakage from a headphone may disturb people around the user depending on the set volume because the user may set the volume so that the user is no longer disturbed by the ambient noise or the user has difficulty recognizing sound leaking to the surrounding environment.
In particular, sound leakage is problematic at places, such as in a train or a bus, where the ambient noise level significantly changes. For example, when a train or a bus is “running”, a user turns up the volume in accordance with the ambient noise since the ambient noise is loud. At this point, sound leakage is hardly recognized by people around the user. However, when the train or the bus “stops” with the volume being kept at the same level, the sound leakage is more likely to be recognized since the ambient noise becomes smaller than that generated when the train or the bus is running.
When the train or the bus is “not running”, the user turns down the volume in accordance with the ambient noise since the ambient noise is smaller than that generated when the train or the bus is “running”. Accordingly, the sound leaking to the surrounding environment is hardly recognized. However, when the train or the bus starts “running”, it is difficult to listen to a musical tune since the ambient noise becomes louder.
In addition, when a user moves to a quiet place, such as a coffee shop, from a loud place, such as a crowded place, where occurrence of sound leakage is hardly recognized by people around the user, the sound leakage is more likely to be recognized by the people around the user.
Furthermore, even if the ambient noise level does not change, sound leakage may occur when a recorded sound level or a music genre that a user is listening to changes in response to a change of musical tunes. For example, a case where a musical tune that the user is listening to while a train or a bus is “running” changes from a quiet musical tune that may be categorized into “classical music” to a musical tune that may be categorized into “rock music” will be discussed. In such a case, the user listens to the “classical music” at a high volume level in accordance with the ambient noise. Since the recorded sound level and the music genre significantly change in response to a change of a musical tune to “rock music”, the user may hurt their ears or people around the user may be more likely to recognize sound leakage.
As described above, when the ambient noise changes or when the playback volume or the genre of a musical tune currently being played back changes, the user adjusts the volume in response to the change in the ambient noise or the musical tune to prevent sound leakage.
Accordingly, recently, a technique, such as an automatic volume limiter system (AVLS), for monitoring a state of a reproduced audio signal and adjusting the volume so that the audio signal level does not exceed a predetermined upper limit has been put to practical use to prevent sound from leaking to the surrounding environment. For example, Japanese Unexamined Patent Application Publication No. 5-49091 discloses a technique for detecting a middle and high audio signal level of an audio signal and adjusting the volume to prevent sound leakage by suppressing the signal level based on the detection result.